(a) Field of the Invention
The present invention relates to roof tiles and more particularly but not exclusively to roof tiles made of a cementitious mixture such as concrete or other material such as clay which are laid in straight or staggered relationship, e.g. so called slate and plain tiles.
(b) Description of the Prior Art
Roof tiles can be made from a cementitious mixture including sand and/or other aggregate, cement, colouring pigment and water plus optionally one or more other additives to facilitate extrusion, prevent growth of fungus, etc. Such tiles have been produced by extrusion for over forty years with apparatus including a hopper-like box which is disposed above a conveyor path and which is charged with the cementitious mixture. The flow of the cementitious mixture is assisted in the box by means of a rotating paddle disposed therewithin. A succession of pallets for moulding the lower surface of the tiles is driven along the conveyor path and beneath the box so that the cementitious mixture forms on the pallets and is compressed therein by means of a rotating roller disposed within the box downstream of the paddle and having a contour which corresponds to the upper surface of the tiles to be formed.
The cementitious mixture is further compressed on the pallets as they pass out of the box by means of a slipper which is disposed downstream of the roller and also has a contour which corresponds to that of the upper surface of the tile to form a continuous extruded ribbon of cementitious mixture on the pallets. The ribbon is subsequently cut into tile forming lengths downstream of the box by means of a suitable cutting knife and the pallets with the formed tiles thereon are conveyed to a curing location. At the curing location, the tiles are conveyed through a curing chamber which is maintained at a high relative humidity and temperature. The curing time is usually in excess of 6 hours. The tiles undergo only a partial curing in the curing chamber from whence they are conveyed to, and stacked, normally out-of-doors, to complete the curing process.
Natural slate and concrete plain tiles are, as is known, laid on the roof in staggered relationship and double lapped, i.e. so that there is always a tile underneath the abutting side edges of adjacent tiles to guard against rain and wind driven water entering into the roof space between the abutting side edges. Traditionally, natural slates have a generally flat geometry with a substantially constant thickness of approximately 10 mm and have a laid weight of approximately 20-40 Kg/m.sup.2. On the other hand, conventional concrete plain tiles have a cambered geometry, a substantially constant thickness of approximately 12 mm and a laid weight of 75 Kg/m.sup.2. With both natural slate and concrete plain tiles the thickness of the visible lower edge, (i.e. that edge which is the lower edge when the tiles are laid in overlapping relationship with a next adjacent line of tiles), when the tiles are laid provides an aesthetically pleasing appearance. However, it has long been an object to avoid the necessity to double lap the tiles to reduce the number of laid tiles per roof and therefore the cost but still retain the aesthetic appearance produced by laying in staggered relationship, and a visible lower edge similar to existing clay and concrete plain tiles, and natural slates, in particular in the case of retiling old roofs.
Applicant's assignee has manufactured interlocking extruded concrete slate tiles which avoid the necessity for double lapping and which have the generally flat geometry of natural slate and a substantially constant edge thickness. However, the lower edge thickness is 25 mm and is necessary in order to provide sufficient strength to avoid breaking off, and to accommodate, the interlocks, i.e. the over and underlocks extending along opposite side edges respectively of each tile. Whilst such concrete slate tiles are designed to be laid in staggered relationship, they are not specified in preference to natural slate and conventional plain tiles because the aesthetic appearance is wrong, i.e. the lower edge thickness is twice that of the optimum required thickness. Furthermore, although the lower surfaces of the tiles have been hollowed out to reduce the weight, the laid weight of these known concrete/interlocking slates is still about 40 to about 60 Kg/m.sup.2 which is considerably more than that of natural slates so that the replacement of natural slates by concrete slates in retiling would require the additional expense of strengthening or replacing the roof timbers.
Even if these known concrete slates were made of material which reduced the weight and thickness of tiles, such a step would decrease the lower edge thickness only down to about 17 to about 20 mm which is still too thick to compete against natural slates and conventional plain tiles.
In the tiles described with reference to, and as illustrated in the drawings of, U.S. Pat. Application Ser. No. 536,591, filed Jun. 28, 1990, the tile lower surfaces are each provided with two or more hanging nibs which enable the tiles to be mounted on battens, fixed to, and extending transversely of, the rafters of a roof, with roof felt interposed therebetween. However, such hanging nibs render the tiles unsuitable for decked pitched roof structures which are in common use in a number of countries, in particular in the U.S. of America. In such pitched roof structures having decking overlying roof rafters, slates, for example, are fixed directly to the decking with there being roof felt interposed between the slates and decking. Whilst, the decking can be continuous, it need not be so. Testing methods, according to the Uniform Building Code Standards, of roofing materials are based on gaps of 5.5 inches between boards spanning the rafters supporting roof tiles. The tiles of the present invention meet these standards.
Accordingly, the main object of the present invention is to provide an interlocking roof tile which can be laid in a straight relationship or a staggered relationship, which can be used for decked pitched roof structures and which can serve as a replacement for slates, shakes or asphalt shingles on such roof structures.